Producing blanks from a single coil of metal has been a cumbersome process. Typically doing so has required multiple slitting lines or a single line that is difficult to adjust.
When multiple lines are used to form blanks, the coil is run through a slitter that slits the coil into narrower coils having the desired width for each blank; then the individual coils are run laterally through another slitter to get the desired length. This method yields wide tolerances as it is difficult to maintain tight control over the dimensions when switching machines.
When a single line is used to form blanks, the coil is slit in a slitter, then the slit strips hang in a looping pit, and a feed roller after the looping pit moves the strip a predetermined distance into a shear. The distance that the strips are fed into the shear corresponds with the desired length of the blank to be cut in the shear. The method of using a single line may seem much simpler than using multiple lines, but it has many difficulties. In this method, a slitter runs at a constant speed, and the slit strips are fed into a looping pit so that the strips may accumulate as the material is stopped at the feed roller during the shearing operation. Differences in material thickness across a coil make feeding the material uniformly into the shear difficult. Uniform feeding of all the strips is necessary to have uniform blanks. Generally, metal coils from the mill are thicker in the center than at the edges. Therefore, a feed roll moving all the slit strips at the same time must move each strip the same distance regardless of its thickness. A machine operator must oftentimes compensate for this by adjusting the amount of force on the opposing feed rolls at various points along their width. It is rarely possible to get all of the strips to feed at exactly the same rate, and this is evident after running some of the coil some distance because the individual slit strips hang at different levels in the looping pit. This slight difference in feed rates means blanks cut from the multiple strips will vary in their length. Additionally, keeping the strips separate as they enter the feed rolls is difficult. Often this requires separators, which are thin rotating metal discs that go between the slit strips. These must be adjusted for each new job which adds to the time to set up the tooling on each job.